1. Field of the Invention
The present invention relates to non-irritating, anhydrous cream vehicles suitable for medicaments having topical therapeutic activity and other dermatological applications.
2. Description of the Prior Art
Pharmaceutical agents effective in topical application, e.g., for treating dermatological conditions, generally must be incorporated into a suitable ointment, lotion or cream vehicle to promote uniform application and effective transdermal absorption.
Originally, most vehicles for topical medicaments were in the nature of greasy ointments which are not water washable and have a tendency to adhere to and stain clothing. Moreover, the greasy composition of many ointments actually inhibits the release and absorption of many topically active pharmaceutical agents.
As an alternative to ointments, water-based creams were developed which are water washable and nonstaining, and yet provide satisfactory spreadability and adherence while not inhibiting the release of active ingredients admixed therewith. These aqueous creams, however, are not suitable for use with active ingredients which are water-decomposable. Furthermore, many of the aqueous creams of the prior art provide little or no occlusive coating to the treated area. In the case of certain topically active agents, such as anti-inflammatory steroids, therapeutic efficacy is substantially increased when the topical vehicle provides occlusion as well as adherence.
In order to combine the desirable unctuousness and pharmaceutical compatability of oil-based ointments with the water miscibility and lightness of aqueous creams, anhydrous water washable vases have been developed which do not adversely affect moisture-degradable ingredients, enable rapid release of the active agent and provide an occlusive coating for enhanced pharmaceutical activity. Such anhydrous creams are disclosed, for example, in U.S. Pat. Nos. 3,592,930 and 3,888,995. The specific cream vehicles described in the aforementioned patents consist primarily of propylene glycol and a saturated fatty alcohol having from 16 to 24 carbon atoms. Various plasticizers, coupling agents and penetrants are also taught as valuable additional ingredients.
While anhydrous creams disclosed in the prior art, e.g., the fatty alcohol/propylene glycol creams, are effective and have been commercially used for topical steroid preparations, they suffer from a number of drawbacks. These creams incorporate fatty alcohols having 16 or more carbon atoms, but commercially available C.sub.16 to C.sub.24 fatty alcohols contain as impurities significant amounts of unsaturated alcohols and alcohols having fewer than 16 carbon atoms. These short-chain alcohols are known irritants which may exacerbate rather than ameliorate the condition to be treated. Moreover, while propylene glycol is the vehicle of choice for many topically active pharmaceuticals, particularly steroids (the higher the propylene glycol concentration, the less need there is for anti-bacterial and anti-fungal preservatives), the propylene glycol concentration in the known anhydrous creams cannot normally be increased beyond about 70% without decreasing the viscosity of the cream to the point where it resembles a lotion.
In addition, the fatty alcohol component of the known anhydrous creams does not enhance the hydrophilic character of the total vehicle. Hence, the prior art anhydrous vehicles do not achieve maximum spreadability upon contact with skin moisture, which is an important factor in patient acceptance of any topical product.